Monte R - 5 layer density

This page is meant to be a "recipe" for the first part of the Density lesson. Information here is not meant for the students, but for teachers who intend to run this demo for their classes. See the attached for a handout for the students.

First Demo: Dueling Drinks.

2 1oz shot glasses
1 waxed playing card

1oz water
1oz syrup 

The goal of this demo is to kick off a larger lesson on the density of liquids. This demo should develop a "need to know" by showing the students a situation they do not normally encounter (liquids usually mix, not trade places). 

Introduce the demo with a short story, for example (abridged): Was at a party with a date, and ran into our crazy friend Quinn. Now, my date was a type one diabetic, so she can't have sugary drinks. I on the other hand love them. Quinn is a practical joker though, and he decides hes going to mess with us a bit, snatches our glasses and practically shouts at us "DO YOU BELIEVE IN SCIENCE!" at this point I figure my drink is totally gone, and I've got to get us both new ones unless I want to risk peeing funny colors...

You should be using this time to set up and perform the demo along with "Quinn" as follows:

Step 1: Set up two 1oz glasses, fill both full (one with syrup, one water)

Step 2: Place the playing card on top of the glass containing the syrup.
Flip it over so that the glass is upside down and on top of the glass filled with water.

Step 3: Align the glasses such that their openings are lined up with each other vertically.

Step 4: begin to remove the playing card. As soon as a space between 
the glasses is opened, the liquids will begin to swap places.

Step 5: Remove card entirely, observe that both liquids are the
 same volume, have switched places, and have not mixed.

Step 6: Reinsert card, carefully! 

Step 7: Using card to keep water in the glass,
 flip the glass back over and remove card.


Gather observations from the class, and then discuss hypotheses that they come up with to explain what happened. Repeat experiment until everyone is satisfied that it's not just a magic trick (in a good class you can even have students try!) and students are confident in their hypotheses. Ask how their hypotheses help predict future outcomes, and why thats a important value for a hypothesis to have.

Lab: Layering Liquids.
In this lab, students are going to put their hypotheses to the test, and see how well they hold up when more variables are added. Students will also demonstrate a understanding of density, and use it in many calculations. 

1 large flower vase (mine holds approx 4 liters)
5 1 liter bottles, clear, labeled A-E (a good permanent marker helps!)
1 Scale 
1 measuring device (not pictured)
assorted food coloring   

Isopropyl alcohol 70%
Vegetable oil
Dish (or hand) soap.
Syrup (any dense water-sugar mix- find something cheap and dark)

Before performing this lab, the teacher will need to measure out known quantities and masses of each substance into the liter sample bottles. Try to randomize the sample letter and volume. Bonus points for making sure the heaviest and densest liquids are different (important distinction!). using food coloring is great for visualization and distinction between clear liquids, but while the liquids won't mix, the food coloring in them will! take note. Getting the highly viscous liquids into the bottles after measuring is problematic (in this case I know not all of the soap made it into the bottle, and my volume is off) Do your best, this data is for you to know as the students do the lab.  

Students will need:
To be divided into 5 groups evenly
1 triple beam balance
1 sample bottle
1 method to mark the volume in container (tape, dry erase marker, ect.)
1 Copy of attached worksheet
access to water.

Students will break into groups, get their supplies, and make observations about their sample liquid (5). Be sure observations include things like color, (apparent) viscosity, and the mass of the container and liquid combined. 

Once each group is done, have each group share their data with the class one at a time and pour their liquid into the vase. Before Pouring make sure the students have marked off how full the bottle was! this will be important soon! Be sure to get some sort of prediction from the class between each sample, and have them write the liquids mass data in a shared location such as a white board.

After all groups have added their sample to the mix, you should have a similar looking result (but larger):

Note: If you worked a bar to get through college, techniques like floating a drink ( and properly pouring a beer ( will be useful to keep the IPA on top (if it mixes with the water, its going to become diluted (changing it's density) and the food coloring will mix, possibly confusing students)

Have the students weigh the bottle again (don't rinse! we want to know how much went into the vase, not how much was in the bottle to start) and use these two masses to find the mass of the liquid now inside the vase.

Now that the mass of the liquid is known, students need to find the volume of the liquid to calculate density. Have students brainstorm ideas (feel free to use student suggestions if they sound plausible- you have back up data for a reason!). My suggested method is to fill the bottle to the marked line again with water (a substance with a known density), find the mass of the water needed to fill the volume, and then calculate the water volume. Plan B; you have the densities figured out already right? So if they figured out the volume wrong, or they didn't have the mark on the bottle they need, (or you know soap is tricky) give that group the density and use that (with the mass) to calculate volume.
Norman Herr,
Feb 24, 2011, 1:05 PM